Polycarbonate and polyester resins have found many commercial uses. Blends of polycarbonate and polyester-based polymers capitalize on the strengths of each polymer and have been found to exhibit excellent physical properties such as rigidity, hardness, scuff resistance, and stability under dynamic and thermal stress. They are also easy to process. A deficiency with these resins is their mechanical properties, especially impact resistance.
Attempts have been made to improve the physical properties through the addition of core-shell impact modifiers. U.S. Pat. No. 4,535,124 discloses the use of a core-shell impact having a bimodal diene or allyl acrylate rubber core. U.S. Pat. No. 5,367,021 discloses a graft copolymer diene rubber core with an optional shell, having particle sizes between 200 and 300 nm. U.S. Pat. No. 5,969,041 discloses a composition having two different core-shell polymer particles, each with a styrene acrylonitrile shell.
A core-shell emulsion polymer having a butadiene-based core and a particle size of from 100 to 200 nm is disclosed in U.S. Pat. No. 6,407,167. All examples of core polymers contained 15-20 percent styrene.
Dispersibility of the core-shell impact modifier combined with the impact resistance, and especially low temperature impact resistance, of the modified polycarbonate/polyester-based resin blends, has not been addressed in the art.
Surprisingly, it has been found that impact resistance of the modifier/polycarbonate/polyester-based resin composition and impact modifier dispersibility is significantly improved when the level of styrene in the core of the core-shell impact modifier is reduced or eliminated.